Abstract: The aim of this experiment was to explore the effects of guanidine acetic acid on growth performance and blood indices of Holstein bulls.A total of 40 2-month-old healthy holstein bulls with similar weight were divided into control group（fed a basal diet） and experimental group（fed a basal diet supplemented with 0.5%GAA additive） with 20 bulls in each group. The experiment lasted for 485 days（2020.07—2021.10）. On the 1 st, 90 th, 275 th, 335 th and 485 th days of the experiment, the cattle was weighed and the average daily gain was calculated. On the 275 th, 460 th and 48 th days of the experiment, blood samples were collected for determination serum biochemical indexes and hormone levels. The results showed that adding 0.5% of GAA in the diet significantly increased the body weight on day 485 and daily gain（P＜0.01） during the whole experiment period, extremely significantly increased the serum TP content（P＜0.01）, significantly decreased serum TG content（P＜0.01）, extremely significantly increased the serum INS level（P＜0.01）, and significantly increased the content of GH in serum（P＜0.05）. These results indicated that adding 0.5% GAA in the diet could promote the growth and reduce fat deposition of Chinese holstein bulls.